滚动事件

     drop.onmousedown = function (event) {
            event = event || window.event;
            var pagex = event.pageX || scroll().left +event.clientX;
            var pagey = event.pageY || scroll().top+event.clientY;
            var x = pagex - box.offsetLeft;
            var y = pagey - box.offsetTop;
            document.onmousemove = function (event){
                event = event || window.event;
                var pagex = event.pageX || scroll().left+event.clientX;
                var pagey = event.pageY || scroll().top+event.clientY;
                var xx = pagex -x;
                var yy = pagey -y;
                box.style.left = xx+"px";
                box.style.top = yy+"px";
            window.getSelection?window.getSelection().removeAllRanges():document.selection.empty();
            }
        };
        drop.onmouseup = function (){
             document.onmousemove = null;
        };
function scroll() {
  return {
    "top" : window.pageYOffset || document.body.scrollTop || document.documentElement.scrollTop,
    "left": window.pageXOffset || document.body.scrollLeft || document.documentElement.scrollLeft
    }
        }
    }